Finish installer with a persistent Rich completion card

[gnulnx]

blc install codex now leaves one horizontally centered Rich completion card in normal terminal scrollback, with the shell prompt directly below it. This replaces the padded checklist reprint and detached onboarding text.

• Share completion content between Rich and plain output, with appropriate guidance for skipped hooks/history, selected steps, failures, and interruptions. JSON output stays machine-readable.
• Remove the cosmetic finalizing step, its obsolete completion-marker requirement, and 3.1 seconds of artificial pauses. Readiness comes from the remaining 11 real checks.
• Update the VHS tape to wait for the final card and returned shell prompt. Reject GIFs at or above 10,000,000 bytes before replacing the previous GIF.

Validation: 191 tests passed, 12 optional integration tests skipped; the GIF size-boundary tests also passed after the final script adjustment. Ruff, Bash syntax, VHS tape validation, and diff checks passed. Recorded and visually reviewed the actual installer flow; all 11 live readiness checks pass.

The refreshed demo is 4,499,779 bytes, 1000×620, 6 fps, and 13.49 seconds. All 81 frames are full and opaque, preserving the fix for stale text between loops.

View the full installer demo

Closes #49.